Comprehensive Molten Aluminum Processing System

ABSTRACT

Molten Aluminum and its Alloys are generally subjected to Degassing and Grain Refining before casting. 
     Degassing is carried out to reduce the Hydrogen gas content. On-line Degassing is among the popular practice and is carried out with the help of equipment like SNIF, LARS etc. 
     Grain refining is carried out for improving the micro-structure of the cast product. It involves addition of grain refiner in to the melt prior to or during the casting. 
     Utility Patent applied vide this non-provisional patent application envisages addition of powder/s of Degasser(Hexa-chloro Ethane), as a substitute for Chlorine and/or Grain refiner; into the purging gas of an On-line Degassing system; thus accomplishing degassing and/or grain refining in one single stage with improved efficacy of respective treatments, better working conditions and lower processing cost. 
     This invention can be adopted in any existing as well as new On-line Degassing systems.

REFERENCE

Provisional Patent Application # 61/216063 Filed on May 12, 2009

BACKGROUND

Molten Aluminum is generally processed before casting for i) removal of Hydrogen dissolved in the melt. This treatment is known as Degassing, and ii) modification of Micro Structure and is known as Grain Refining.

Degassing

Degassing is a common practice to reduce the Hydrogen gas content of molten Aluminum and its Alloys.

Among the earliest practices of the degassing has been to treat the melt (molten Aluminum/Aluminum Alloy) with Hexa-chloro Ethane. Here-in, degassing is affected by Chlorine gas which emanates from decomposition of the Hexa-chloro Ethane on its purging through the melt.

In order to improve the efficacy of removal of Hydrogen, as also for operational convenience and containment of environmental hazards; On-line Degassing has been adopted by the industry.

In On-line Degassing, Nitrogen or inert gas like Argon is purged through the melt with the help of specially designed rotating nozzles which enables the dissolved Hydrogen to come out of the melt as bubbles. Some such equipment available in the market for this purpose are SNIF, LARS etc.

In the later developments, small percentage of Chlorine has been added to the purging gas. This has helped in improving the efficacy of degassing process and thus has gained acceptance. However, addition of Chlorine has its own complications and hazards in addition to the cost.

Grain Refining

Grain refining of aluminum and its alloys is carried out for improving the micro-structure of the cast product so as to improve the casting rate, resistance to hot cracking, and mechanical properties, particularly the toughness and ductility, etc.

Describing briefly the metallurgy behind grain refining, Nucleants or Grain Refiners (here-in after referred to as Gain Refiner) when introduced into molten Aluminum and its Alloys; increase the number of sites available for formation of grains. In such condition, more grains are formed at the cost of size of individual grains. Thus the micro-structure of the material will have smaller/finer grains and hence better mechanical properties.

Commonly used Grain Refiners are of two types:

Metal based e.g. Alloys of Aluminum with Titanium and Boron, and;

Chemicals—Complex salts generally sold as proprietary chemicals.

Pre-requisite for efficacy of a grain refining is its ability to provide nucleation sites in the molten metal prior to casting and their uniform dispersion which ensures uniformity in micro structure and hence uniform properties.

While the ability to impart nucleation sites is a characteristic of the grain refine, its dispersion in the molten metal (melt) largely depends on processing practice and is ensured by gradual addition and/or through mixing into the molten metal bath. Continuous addition of Grain Refiners has been widely adopted by the industry, but this practice as been confined to metal based Grain Refiners; which are available as rods in coil form and the addition of grain refiner is an independent process.

SUMMARY

Removal of dissolved Hydrogen and Grain Reining are commonly accepted practices to process molten Aluminum and Its Alloys before casting.

Utility Patent applied vide this provisional patent application envisages addition of Degasser and/or Grain refiner on a continuous basis along with the on-line degassing there by accomplishing degassing and grain refining in one single stage.

Unique features of this invention are:

Degassing

Chlorine gas, which at present is mixed with/added to the purging gas in on-line degassers of Aluminum and its Alloys, is substituted by Hexa-chloro Ethane.

The Hexa-chloro Ethane is envisaged to be mixed with/added to the purging gas as powder—micronized or pulverized.

Addition of Hexa-chloro Ethane as a substitution for Chorine is expected to yield favorable techno-economics and safer working conditions.

Grain Refining

As per this invention, Grain refining is envisaged to be carried out simultaneously with the on-line degassing. This is envisaged to be accomplished by addition of the grain refiner to the purging gas.

Grain refiner is envisaged to be used as Powder only, and thus the Invention can be adapted for Grain Refiners which are either available as powder or can be powdered before use.

The grain refiner when introduced into molten metal (melt) along with the purging gas will have significantly improved dispersion in the molten metal and will not have enough time to coagulate. Thus there will be ideal conditions for grain refining, with the improved efficacy of the treatment. On a net basis, the specific consumption of nucleant or grain refiner, for identical results; will be significantly lower as compared to the conventional practices.

There will also be substantial saving in cost of Grain Refiner because of lower cost of Nucleant or Grain Refining Chemicals.

THE INVENTION

The invention relates to a practice envisaging addition of Degasser and/or Grain refiner on a continuous basis along with the purging gas of the on-line degassing system.

Schematic representation of the process envisaged in this invention is as below:

Dispenser (for continuous supply of Hexa-chloro Ethane and/or Grain Refiner) + Purging gas (Nitrogen or → Gas intake of →Purging into Argon or any other On-line Degassing Molten Aluminum inert gas) system or its Alloys

As it can be inferred from the schematic representation the practice, degasser (Hexa-chloro Ethane) and/or grain refiner is added to the purging gas (Nitrogen and/or Argon or any other inert gas) before the on-line degassing system.

The mixture of purging gas and degasser and/or grain refiner are introduced into molten aluminum or its alloys (melt) with the help of an on-line degassing system. In other words, the purging gas carries the degasser and/or nucleant or grain refiner into the On-line degassing system and ultimately into the melt.

The Hexa-chloro Ethane and/or Nucleant or Grain Refiner is/are envisaged to be mixed with/added to the purging gas as powder with the help of a dispenser.

The dispenser unit is suitably attached to/integrated with the on-line degassing system.

This invention intends to use the developments that have taken place in On-line Degassing systems which are available for degassing of molten Aluminum and its Alloys on commercial basis.

Addition of Hexa-chloro Ethane and/or Grain Refiner in the proposed manner, are expected to yield favorable techno-economics without compromising on safe working conditions.

BENEFITS OF THE INVENTION

The invention is expected to provide an alternative of Chlorine for on-line degassing of molten Aluminum and its Alloys. Adoption of the invention will also be cost effective and alleviate hazards associated with use of Chlorine without any loss of efficacy.

Addition of grain refiner to the purging gas will significantly improve its dispersion in the molten metal and will not have enough time to coagulate. Thus there will be ideal conditions for grain refining, with the improved efficacy of the treatment. On a net basis, the specific consumption of grain refiner, for identical results; will be significantly lower as compared to the conventional practices.

There will also be substantial saving in cost of Grain Refiner because of lower cost of Grain Refining Chemicals.

APPLICABILITY

This invention can be adopted in any existing on-line degassing systems intended for removal of Hydrogen gas of molten Aluminum and its Alloy; as also the ones to be manufactured in future. 

1. The invention titled as Comprehensive Molten Aluminum Processing System is envisaged to provide an alternative of Chlorine for on-line degassing of molten Aluminum and its Alloys. Adoption of the invention will also be cost effective and alleviate hazards associated with use of Chlorine without any loss of efficacy.
 2. Addition of grain refiner to the purging gas will significantly improve its dispersion in the molten metal and will not have enough time to coagulate. Thus there will be ideal conditions for grain refining, with the improved efficacy of the treatment. On a net basis, the specific consumption of grain refiner, for identical results; will be significantly lower as compared to the conventional practices.
 3. (canceled)
 4. This invention can be adopted in any existing on-line degassing systems intended for removal of Hydrogen gas of molten Aluminum and its Alloy; as also the ones to be manufactured in future. 